Method of and apparatus for viewing an image

ABSTRACT

Light from an image displayed on a display screen  10  is transmitted to an observer&#39;s eye  11  by way of a dynamic optical element  12  (such as a spatial light modulator or an electrically switchable holographic composite) which acts as a lens. The characteristics of the dynamic optical element  12  can be altered so that it acts sequentially to direct light of different colors to the observer&#39;s eye. 
     In one optional embodiment emitters  17  on the display screen  10  emit infra-red radiation which is projected by the dynamic lens  12  as a broad wash onto the eye  11.  Infra-red radiation reflected back from the eye  11  is focussed by the dynamic lens  12  onto detectors  18  also provided on the display screen  10.  The detectors  18  are thus able to sense the direction of eye gaze, and the dynamic lens  12  is controlled in dependence on this to create an area of high resolution in an area of interest centered on the direction of gaze, which is moved to follow the eye gaze as its direction alters. Other than in the area of interest, the dynamic lens  12  has a relatively low resolution.

This application is a continuation-in-part of International ApplicationPCT/GB97/00711 filed Mar. 14, 1997, which designated the United States.

FIELD OF THE INVENTION

This invention relates to a method of and apparatus for viewing animage.

BACKGROUND OF THE INVENTION

In head-mounted optical displays (such as are used in the recreationindustry for viewing virtual reality images), it has been the practiceto project an image to be viewed into the observer's eyes usingconventional refractive and reflective optical elements, i.e. lenses andmirrors. However, in head-mounted displays where weight and size aremajor considerations it is normally possible to provide only a verysmall field of view by this means, which is a disadvantage when it isdesired to provide the observer with the sensation of being totallyimmersed in a virtual world. In an attempt to overcome this problem, ithas been proposed to use so-called “pancake windows”, i.e. multi-layerdevices which use polarisation and reflection techniques to simulate theeffect of lenses and mirrors. However, such devices suffer from theproblem that they have low transmissivity.

Particularly with the factors of size and weight in mind, wide fieldoptics designs have turned to diffractive optical solutions. It is knownthat diffractive techniques can be used to simulate the effect of alens, by reducing the profile to a kinoform (FIGS. 1 and 2) or by theuse of fixed surface or volume holograms. However diffractive opticshave always suffered from extreme chromatic aberration when used in fullcolour imaging systems. Correction methods which have includedmultiplexing holograms recorded with different wavelengths in a singleemulsion have been suggested. Such schemes still exhibit residualcrosstalk between the colour channels which makes them inappropriate forhigh quality imaging systems.

Additionally, wide fields of view lead to problems in other forms ofaberration correction, as well as difficulties in supporting the databandwidth required to support high resolution across the entire field ofview.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of andapparatus for viewing images which improve on the techniques describedabove.

According to a first aspect of the present invention, there is provideda method of viewing an image, the method comprising transmitting animage into an eye of an observer by means of a dynamic optical device,the dynamic optical device being operative to create a modulation inrespect of at least one of phase and amplitude in light transmitted orreflected thereby, said modulation being variable from one point orspatial region in the optical device to another, and wherein themodulation at any point or spatial region can be varied by theapplication of a stimulus, and altering the characteristics of thedynamic optical device so that the dynamic optical device actssequentially to direct light of different colours to the observer's eye.

The expression “transmitting an image” is intended to include theformation of a virtual aerial image at some point, or the projection ofa real image onto the surface of the observer's retina.

According to a second aspect of the present invention, there is providedapparatus for viewing an image, comprising a dynamic optical device, thedynamic optical device being operative to create a modulation in respectof at least one of phase and amplitude in light transmitted or reflectedthereby, said modulation being variable from one point or spatial regionin the optical device to another, and control means operative to apply astimulus to the dynamic optical device, whereby the modulation at anypoint or spatial region can be varied, the control means being operativeto alter periodically the characteristics of the dynamic optical deviceso that the device acts sequentially to direct light of differentcolours to the observer's eye.

The dynamic optical device can comprise a succession of layers which areconfigured to act upon the primary wavelengths, respectively, or thedifferent colour channels may all be embodied in the one layer of thedynamic optical device.

Moreover, the optical power (focal length), size, position and/or shapeof the exit pupil and other optical parameters can also be controlled.

The above-described method and apparatus allow the provision not only ofa relatively wide field of view, but also a large exit pupil, a movableexit pupil of variable shape, and high resolution.

Conveniently, the dynamic optical device comprises a spatial lightmodulator containing an array of switchable elements in which theoptical state of each element can be altered to create a change in phaseand/or amplitude in the light incident thereon. Alternatively, thedynamic optical device can comprise an array of switchable prerecordedholographic elements, wherein more complex phase functions can beencoded within the holograms. In this case, the dynamic optical devicecan also comprise non-switchable holographic elements.

Advantageously, the dynamic optical device comprises an electricallyswitchable holographic composite.

Desirably, the dynamic optical device is used in a range in which thephase and/or amplitude modulation varies substantially linearly withapplied stimulus.

The dynamic optical device is preferably used in a range in which itdoes not substantially affect the amplitude and/or wavelengthcharacteristics of the light transmitted or reflected thereby.

The dynamic optical device can be in the form of a screen adapted formounting close to the observer's eye. The screen can be of generallycurved section in at least one plane. Alternatively, for ease ofmanufacture, the screen may be planar. Conveniently, the apparatus alsocomprises means for engaging the screen with the observer's head in aposition such that the curve thereof is generally centred on the eyepoint.

In one arrangement, the dynamic optical device acts upon lighttransmitted therethrough, and the image generator is located on a sideof the dynamic optical device remote from the intended position of theobserver's eye. In an alternative arrangement, the dynamic opticaldevice acts upon light reflected thereby, and the image generator is atleast partially light-transmitting and is located between the dynamicoptical device and the intended position of the observer's eye.

The apparatus may include image generation means configured off-axisfrom the general direction of the observer's eye in use. In that case,the image generation means can be non-light transmitting.

In one arrangement, the dynamic optical device comprises a plurality ofdiscrete optical elements in close juxtaposition to each other, each ofwhich acts as an individual lens or mirror. Conveniently, some of thediscrete optical elements act to direct to the observer's eye light ofone colour, while others of the discrete optical elements act to directto the observer's eye light of other colours.

In one preferred embodiment of the invention, the apparatus may compriseleft and right image generation means, left and right dynamic opticaldevices and left and right side portions within which said left andright image generation means are housed, said left and right imagegeneration means being operative to project towards said left and rightdynamic optical devices respectively, thereby displaying a binocularimage. The apparatus can also be arranged to provide for the full rangeof accommodation and convergence required to simulate human vision,because the parameters governing the factors can be altered dynamically.

Advantageously, the dynamic optical device functions to correctaberrations and/or distortions in the image produced by the imagegenerator. The dynamic optical device can also function to create adesired position, size and/or shape for the exit pupil.

The method may further comprise the steps of controlling thecharacteristics of the dynamic optical device to create an area ofrelatively high resolution in the direction of gaze of the observer'seye, the dynamic optical device providing a lesser degree of resolutionof the image elsewhere, and sensing the direction of gaze of theobserver's eye and altering the characteristics of the dynamic opticaldevice in accordance therewith, so that the area of relatively highresolution is repositioned to include said direction of gaze as thelatter is altered.

The apparatus may further comprise sensing means operative to sense thedirection of gaze of the observer's eye, and the control means beingoperative on the dynamic optical device to create an area of relativelyhigh resolution in said direction of gaze, the dynamic optical deviceproviding a lesser degree of resolution of the image elsewhere, thecontrol means being responsive to the sensing means and being operativeto alter the characteristics of the dynamic optical device to move saidarea of relatively high resolution to follow said direction of gaze asthe latter is altered.

Moreover, in accordance with a third aspect of the invention, there isprovided apparatus for viewing an image, comprising a dynamic opticaldevice, the dynamic optical device being operative to create amodulation in respect of at least one of phase and amplitude in lighttransmitted or reflectual thereby by means of which the observer's eyeviews an image in use, sensing means operative to sense the direction ofgaze of the observer's eye, and control means which acts on the dynamicoptical device to create an area of relatively high resolution in saiddirection of gaze, the dynamic optical device providing a lesser degreeof resolution of the image elsewhere, the control means being responsiveto the sensing means and being operative to alter the characteristics ofthe dynamic optical device to move said area of relatively highresolution to follow said direction of gaze as the latter is altered.

It will be appreciated that the features identified above as beingpreferred features of the second aspect of the invention may also beincorporated into the apparatus of the third aspect of the invention.

Preferably, the sensing means utilises radiation which is scattered fromthe observer's eye and which is detected by detector means, and thedynamic optical device may also function to project said radiation ontothe eye and/or to project to the detector means the radiation reflectedby the eye.

Conveniently, the sensing means includes a plurality of sensors adaptedto sense the attitude of the observer's eye, the sensors beingpositioned in or on the dynamic optical device and/or the imagegenerator.

Preferably, the sensing means comprises emitter means operative to emitradiation for projection onto the observer's eye and detector meansoperative to detect radiation reflected back from the eye.

Desirably, the sensing means utilises infra-red radiation. In this casethe dynamic optical device can be reconfigured to handle visible lighton the one hand and infra-red radiation on the other.

The apparatus can further comprise at least one optical element providedin tandem with the dynamic optical device, which acts upon infra-redlight but not upon visible light.

The detector means can be provided on a light-transmitting screendisposed between the image generator and the dynamic optical device.

Conveniently, a reflector is disposed between the image generator andthe light-transmitting screen, and is operative to reflect the infra-redradiation whilst allowing transmission of visible light, such that theinfra-red radiation after reflection by the observer's eye passesthrough the dynamic optical device and the light-transmitting screen,and is reflected by said reflector back towards the screen.

In cases where the sensing means operates on infra-red principles, it isnecessary to focus onto the detectors the returned infra-red radiationafter reflection from the observer's eye. Although it is possible toemploy for this purpose the same optical elements as are used to focusthe image light onto the observer's eye, the disparity in wavelengthbetween visible light and infra-red radiation means that this cannotalways be achieved effectively. According to a development of theinvention, the sensing function is performed not by infra-red radiationbut rather by means of visible light. The light can be renderedundetectable by the observer by using it in short bursts. Alternatively,where the emitter means is provided at pixel level in the field of view,the wavelength of the light can be matched to the colour of thesurrounding elements in the image. As a further alternative, the lightcan be in a specific narrow band of wavelengths. This technique also hasapplicability to viewing apparatus other than that including dynamicoptical devices, and has a general application to any apparatus whereeye tracking is required.

Preferably, the emitter means and/or the detector means are provided ona light-transmitting screen disposed between the image generator and thedynamic optical device.

Desirably, the image generator is in the form of a display screen, andthe emitter means and/or the detector means are provided in or on thedisplay screen.

Conveniently, the emitter means are provided in or on the displayscreen, a beamsplitter device is disposed between the display screen andthe dynamic optical device and is operative to deflect radiationreflected by the observer's eye laterally of the main optical paththrough the apparatus, and the detector means are displaced laterallyfrom the main optical path.

Where the image generator produces a pixellated image, the emitter meansand/or detector means can be provided at pixel level within the field ofview.

Advantageously, the image generator and the dynamic optical device areincorporated into a thin monolithic structure, which can also include amicro-optical device operative to perform initial bean shaping. Themonolithic structure can also include an optical shutter switchablebetween generally light-transmitting and generally light-obstructingstates.

The apparatus can further comprise means to permit the viewing ofambient light from the surroundings, either separately from or inconjunction with the image produced by the image generator. In thiscase, the image generator can include discrete light-emitting elements(such as lasers or LEDs) which are located on a generallylight-transmitting screen through which the ambient light can be viewed.

Preferably, the light-emitting elements of said device are located atthe periphery of said screen, and the screen acts as a light guidemember and includes reflective elements to deflect the light from thelight-emitting elements towards the dynamic optical element.

Desirably, the image generator is in the form of a display panel, andthe panel is mounted so as to be movable between a first position inwhich it confronts the dynamic optical device and a second position inwhich it is disposed away from the dynamic optical device.

In an alternative arrangement, the image generator is in the form of adisplay screen and displays an input image, and the apparatus furthercomprises detector means operative to sense the ambient light, aprocessor responsive to signals received from the detector means todisplay on the display screen an image of the surroundings, and meansenabling the display screen to display selectively and/or in combinationthe input image and the image of the surroundings.

In one particular arrangement, the image generator comprises an array oflight-emitting elements each of which is supplied with signalsrepresenting a respective portion of the image to be viewed, wherein thesignals supplied to each light-emitting element are time-modulated withinformation relating to the details in the respective portion of theimage, and the area of relatively high resolution is produced by meansof the dynamic optical device switching the direction of the light fromthe light-emitting elements in the region of the direction of gaze ofthe observer's eye.

The apparatus can further comprise tracking means operative to track thehead positions of a plurality of observers, and a plurality of sensingmeans each of which is operative to detect the direction of eye gaze ofa respective one of the observers, with the dynamic optical device beingoperative to create a plurality of exit pupils for viewing of the imageby the observers, respectively.

The image produced by the image generator can be pre-distorted to lessenthe burden on the dynamic optical device. In this case, the distinctionbetween the image display and the dynamic optical device is less welldefined, and the functions of the image generator and the dynamicoptical device can be combined into a single device, such as a dynamichologram. More particularly, a spatial light modulator can be used toproduce a dynamic diffraction pattern which is illuminated by one ormore reference beams.

Preferably, said image for viewing by the observer is displayed on adisplay screen, which can be of generally curved section in at least oneplane. The apparatus can further comprise means for engaging the displayscreen with the observer's head in a position such that the curvethereof is generally centred on the eye point.

The apparatus can form part of a head-mounted device.

In a preferred arrangement as described above, the dynamic opticaldevice functions not only to focus image light onto the observer's eye,but also to project radiation from the emitters onto the eye, and/or toproject the radiation reflected by the eye onto the detectors. Accordingto a fourth aspect of the present invention, this general technique canbe applied to viewing apparatus in which conventional optics rather thana dynamic optical device are employed.

Thus, according to the said fourth aspect of the invention, viewingapparatus comprises an image generator operative to generate an imagefor viewing by an observer's eye, an optical system for transmittingsaid image to the observer's eye position, sensing means operative tosense the direction of gaze of the observer's eye, and control meansresponsive to the sensing means and operative to act on the imagegenerator and/or the optical system to modify said image transmitted tothe eye in accordance with the direction of gaze of the eye, the sensingmeans including emitter means operative to emit radiation for projectiononto the observer's eye, and detector means operative to detect saidradiation after reflection by said eye, the optical system alsofunctioning to transmit said radiation from the emitter means onto saideye and/or to transmit said radiation reflected from said eye to thedetector means.

Preferably, said radiation comprises infra-red radiation.

In a particular arrangement, the optical system includes at least oneoptical element which acts upon both visible light and infra-redradiation, and at least one second optical element which acts uponinfra-red radiation but not upon visible light. In this way, the opticalsystem can have a different focal length for visible light than that forinfra-red radiation.

In one embodiment, the detector means (and preferably also the emittermeans) are provided on a light-transmitting screen disposed between theimage generator and the optical system. Desirably, a reflector (such asa holographic/diffractive reflector or a conventional dichroicreflector) is disposed between the image generator and thelight-transmitting screen, and is operative to reflect the infra-redradiation whilst allowing transmission of visible light, such that theinfra-red radiation after reflection by the observer's eye passesthrough the optical system and the light-transmitting screen, and isreflected by said reflector back towards the screen.

In the case where the image generator is in the form of a displayscreen, the emitter means and/or the detector means can be provided inor on the display screen. Alternatively, the emitter means can beprovided in or on the display screen, a beamsplitter device can bedisposed between the display screen and the optical system so as todeflect infra-red radiation reflected by the observer's eye and passingthrough the optical system laterally of the main optical path throughthe apparatus, and the detector means can be displaced laterally fromsaid main optical path.

Advantageously, the image generator generates a pixellated image, andthe emitter means and/or the detector means are provided at pixel level.

In a preferred arrangement as described above, the sensing meanscomprises emitters and detectors provided at pixel level within thefield of view. According to a fourth aspect of the present invention,this general technique can be applied to viewing apparatus in whichconventional optics rather than a dynamic optical device are employed.

Thus, according to the said fourth aspect of the invention, viewingapparatus comprises an image generator operative to generate an imagefor viewing by an observer's eye, an optical system for transmittingsaid image to the observer's eye position, sensing means operative tosense the direction of gaze of the observer's eye, and control meansresponsive to the sensing means and operative to act on the imagegenerator and/or the optical system to modify said image transmitted tothe eye in accordance with the direction of gaze of the eye, the sensingmeans including emitter means operative to emit radiation for projectiononto the observer's eye, and detector means operative to detect saidradiation after reflection by said eye, the emitter means and/or thedetector means being provided at pixel level within the field of view ofthe image.

Particularly in the case where the image generator is in the form of adisplay screen, the emitter means and/or the detector means can beprovided at pixel level in or on the display screen. Alternatively, theemitter means and/or the detector means can be provided at pixel levelon a light-transmitting screen disposed between the image generator andthe optical system.

Preferably, said radiation comprises infra-red radiation.

In a particular arrangement, the optical system includes at least oneoptical element which acts upon both visible light and infra-redradiation, and at least one second optical element which acts uponinfra-red radiation but not upon visible light. In this way, the opticalsystem can have a different focal length for visible light than that forinfra-red radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only,with reference to the remaining Figures of the accompanying drawings, inwhich:

FIG. 1 is a schematic view of a kinoform lens of known type;

FIG. 2 is a graphical arrangement of a kinoform lens, demonstrating howthe lens can be implemented in practice;

FIG. 3 is a general arrangement drawing illustrating a viewing apparatusand method according to the present invention;

FIG. 4 is a schematic view of a first embodiment of viewing apparatusaccording to the present invention;

FIG. 4A is a detail of part of the apparatus shown in FIG. 4;

FIGS. 4B to 7 are graphs illustrating various characteristics of theapparatus of FIG. 4;

FIG. 8 is a schematic view of a modification to the first embodiment ofthe viewing apparatus;

FIG. 8A is a detail of part of the apparatus shown in FIG. 8;

FIG. 9 is a schematic view of a second embodiment of viewing apparatusaccording to the present invention;

FIG. 10 is a schematic view of a modification to the second embodimentof the viewing apparatus;

FIG. 11 illustrates a third embodiment of viewing apparatus according tothe invention, which uses an electrically switchable holographiccomposite (ESHC);

FIGS. 11A and 11B illustrate the operation of the ESHC;

FIGS. 12 and 13 illustrate the use of an alternative form of imagegenerator in the apparatus;

FIGS. 14 and 15 show arrangements enabling the viewing of thesurroundings in addition to a displayed image;

FIGS. 16 to 18 are schematic views of further embodiments of viewingapparatus according to the invention, showing in particular an eyetracker;

FIG. 19 is a diagram illustrating the general principle of a dynamicoptical device as embodied in the viewing apparatus;

FIG. 20 is a diagram illustrating the use of a dynamic hologram;

FIGS. 21 and 21A illustrate the use of planar display screens anddynamic optical devices;

FIG. 22 is an exploded perspective view of apparatus for viewing animage, employing an ESHC as the dynamic optical device;

FIG. 23 is a schematic section through the apparatus shown in FIG. 22;

FIG. 24 is a schematic sectional view of an arrangement wherein theapparatus is of generally curved configuration;

FIG. 25 is a schematic sectional view of another embodiment of theapparatus;

FIG. 26 is a schematic sectional view of part of an image generator;

FIGS. 27A, 27B and 27C are schematic views of different opticalarrangements for the apparatus;

FIG. 28 is a schematic view of apparatus for use by multiple observers;

FIGS. 29 and 30 are schematic plan views of apparatuses for use indisplaying stereoscopic images;

FIGS. 31 to 35 show a further embodiment of viewing apparatus accordingto the present invention, and

FIGS. 36. 36A and 36B show a modification of the embodiment depicted inFIGS. 31 to 35.

FIG. 37 is a perspective schematic diagram of a further specificembodiment of apparatus in accordance with the invention;

FIG. 38 is a plan view of the apparatus illustrated in FIG. 37;

FIG. 39 is a plan view of a yet further specific embodiment of apparatusin accordance with the invention; and

FIG. 40 is a view of the dynamic optical device of the apparatusillustrated in FIG. 39, in use, in the direction indicated by arrows Xin FIG. 39;

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring to FIG. 3, there is shown a general arrangement of viewingapparatus which comprises a display screen 10 on which is displayed animage to be viewed by an eye 11 of an observer. Interposed between thedisplay screen 10 and the eye 11 is a dynamic optical element (in thiscase, a lens) in the form of a screen 12. The dynamic lens comprises aspatial light modulator (such as a liquid crystal device) to which astimulus is applied by a control device 13 to create an area ofrelatively high resolution in the direction of gaze of the eye 11, theremaining area of the modulator providing a lesser degree of resolution.Sensing means 14 is operative to sense the attitude of the eye 11, andthe control device 13 is responsive to signals received from the sensingmeans 14 and alters the characteristics of the modulator so that thearea of relatively high resolution is moved so as to follow thedirection of gaze of the observer's eye 11 as this is altered.

The apparatus and its characteristics will now be described in moredetail. Although the described apparatus is intended for use in ahead-mounted device for viewing virtual reality images, it will beappreciated that the apparatus has many other uses and applications aswell.

In the ensuing description,. reference will be made to the apparatus asbeing applied to one of the observer's eyes. However, when used forvirtual reality applications, two such apparatuses will in fact beprovided, one for each eye. In this case, the respective display screenscan (if desired) be used to display stereoscopic images to provide a 3-Deffect to the observer.

FIGS. 4 and 4A show a first actual embodiment of the viewing apparatus,wherein similar components are designated by the same reference numeralsas used in FIG. 3. However, the control device 13 and the sensing means14 are omitted for the sake of clarity. In this embodiment, the displayscreen 10 and the screen 12 are each of curved configuration and arecentred generally on the rotation axis of the observer's eye 11.

The spatial light modulator comprising the screen 12 can operate onphase and/or amplitude modulation principles. However, phase modulationis preferred because amplitude modulation devices tend to haverelatively low light efficiency. The modulator has a phase modulationdepth of not less than 2 and its phase shift varies linearly withapplied voltage.

The aperture and focal length of the dynamic lens formed by the spatiallight modulator, are dictated by the resolution of the modulator. Theform of the lens is modified in real time, allowing the focal length tobe changed so that conflicts between accommodation and convergence canbe resolved. In addition, focus correction for different users can becarried out electronically rather than mechanically.

The dynamic lens is intended to provide an area of interest (AOI) fieldof view, the AOI being a high resolution region of the field of viewthat corresponds to the instantaneous direction of gaze of theobserver's eye. By reducing the size of the AOI, certain benefits arisesuch as minimising the amount of imagery that needs to be computed fordisplay on the screen 10 at any instant, improving the image quality byallowing the dynamic lens to operate at low field angles, and increasingthe effective image brightness and resolution of the display. FIG. 4Bshows in graphic form the variation of resolution across the AOI.

Normally, the optics required to achieve human visual fields of viewinvolve very complex optical designs consisting of many separate lenselements. The concept employed in the present invention achieves economyof design by using an adaptive lens in which its transform is recomputedfor each resolution cell of the field of view. Furthermore, since thedynamic lens is used with a device (eye tracker) which senses theattitude of the observer's eye, only a modest AOI is required.Accordingly, the form of the lens is simplified, although separate lensforms are required for each increment in the field of view to ensurethat collimation is preserved over the entire field of view.

The diffractive principles employed by the spatial light modulator areideally suited to correcting for monochromatic aspheric and high orderspherical aberrations, distortion, tilt and decentring effects. However,since diffractive structures suffer from chromatic aberration, it isnecessary to compute separate forms for each wavelength, and inparticular to re-compute the diffraction pattern for each of the primarywavelengths used in the display. For example, in one arrangement thedynamic optical device is configured to produce an array of discretemicro-lenses in close juxtaposition to each other, with some of themicro-lenses acting to direct to the observer's eye red light, whilstother micro-lenses act to direct green and blue light to the observer'seye, respectively. In a second arrangement, the characteristics of thedynamic optical device are altered periodically so that, at least in thearea of high resolution, it acts to direct to the observer's eye red,green and blue light in temporal sequence. In a third arrangement, thedynamic optical device comprises several layers which are designed toact on red, green and blue wavelengths, respectively. The resolution ofthe apparatus is dependent upon several factors, especially thedimensions of the dynamic lens, the resolution of the spatial lightmodulator, the number of phase levels in the spatial light modulator,focal length and pixel size of the display screen 10. In order toachieve a satisfactory resolution, the dynamic lens is operated not as asingle lens, but rather as an array of micro-lenses as depictedschematically at 12 a in FIG. 4.

Diffracting structures are subject to similar geometric aberrations anddistortions to those found in conventional lenses. By using an eyetracker in conjunction with an area of high resolution in the dynamiclens, the effects of distortion are minimal, particularly since lowrelative apertures are used. Generally, diffractive optics are moredifficult to correct at high optical powers. From basic aberrationtheory, the field angle achievable with the dynamic lens is limited to afew degrees before off-axis aberrations such as coma start to becomesignificant and it becomes necessary to re-compute the diffractionpattern.

In general, the correction of geometric distortions and matching of theAOI with lower resolution background imagery can be carried outelectronically. Particularly in the case where the dynamic lens isimplemented in a curved configuration (as depicted in FIG. 4), theeffects of geometric distortion will be minimal.

The main factors affecting transmission through the dynamic lens are thediffraction efficiency, effective light collection aperture of theoptics, and transmission characteristics of the medium employed for thedynamic lens. Because of the geometry of the dynamic lens, the effect ofocclusions and vignetting will be minimal. The most significant factortends to be the collection aperture. In order to maximise thetransmission of the display to the dynamic lens, it is possible toinclude an array of condensing lenses. FIG. 4A shows a detail of thedisplay screen 10 depicted in FIG. 4, wherein an array 15 ofmicro-lenses is disposed in front of the display screen 10 to performinitial beam-shaping on the light emitted from the screen, before thisis transmitted to the dynamic lens. Alternatively, this beam-shapingfunction can be performed by means of diffractive or holographiccomponents.

Because the operation of the dynamic lens is governed by the attitude ofthe observer's eye, the majority of the processing of the imagedisplayed on the screen 10 at any one time will be concerned with theimage region contained in the exit pupil. To take full advantage of theeye's visual acuity characteristics, the eye tracker is arranged tooperate at bandwidths of at least 1000 Hz in order to determine thetracking mode of the eye (for example smooth pursuit or saccade).

The picture content in the exit pupil of the dynamic lens at any giventime will depend upon the AOI field of view, and the field angle andresolution of the dynamic lens. FIG. 5 shows in graphic form acalculation of the number of resolution cells in the exit pupil thatwill need to be up-dated per frame as a function of the AOI fordifferent values of the dynamic lens field angle. For the purpose ofthese calculations, it has been assumed (for illustrative purposes) thatthe dynamic lens consists of 20×20 micro-lenses each of 0.5 mm size,with each micro-lens having a resolution of 48×48. It has also beenassumed that the dynamic lens has a field of view of 7°, and that theAOI is 10°. This results in a total of about one million cells in theexit pupil, equivalent to a 1000×1000 array. Taking into account thedynamic lens field angle, each of these cells will need to be up-datedapproximately 2 times per frame, i.e. 2 million cell up-dates per frameare required. By extrapolating from the size of the exit pupil to themaximum array size necessary to provide the same resolution over anentire field of view of, say, 135°×180°, it can be determined that adynamic lens comprising of the order of 113×113 micro-lenses will berequired (equivalent to a 5400×5400 cell spatial light modulator).

The specification of the input image display (i.e. the image asdisplayed on the screen 10) will be determined by the required displayresolution. For example, by aiming to match the 1 minute of arcresolution of the human visual system, the display will need to providea matrix of 8100×8100 pixels to achieve the desired performance over afield of view of 135°×180°. The number to be up-dated in any given framewill be considerably smaller. FIG. 6 shows in graphic form the number ofactive display elements required in the exit pupils, assuming a variableresolution profile of the form shown in FIG. 7.

Significant economy in the computation of the input imagery can beachieved by exploiting the rapid fall-off of human visual acuity withangle. Since only 130,000 pixels can be observed by the eye at any time,and noting that the eye is not very good at distinguishing intermittentevents at moderate rates (typically 30 per second), it can be concludedthat the apparatus of the present invention presents a processingrequirement which is not significantly bigger than that of a 625 linetelevision.

The exit pupil of the dynamic lens is not subject to the same physicalconstraints as that of a conventional lens system, since it is definedelectronically. According to the normal definition of the term, it couldbe said that the exit pupil covers the whole of the 135°×180° field ofview. However, because of the eye tracking function employed in thepresent invention, it is more appropriate to consider the exit pupil asbeing the region of the spatial light modulator array contained withinthe eye-tracked area of interest. The remainder of the field of view isfilled with imagery whose resolution progressively decreases as theperiphery is approached.

FIG. 8 illustrates a particular manner of implementing the eye trackingfunction, with similar components being accorded the same referencenumerals as employed in FIG. 4. In this embodiment, the eye trackingfunction is achieved by means of an array of emitters 17 and detectors18 provided on a screen 19 disposed immediately in front of the displayscreen 10. Radiation (such as infra-red radiation) is emitted by theemitters 17 and is directed by the dynamic lens 12 as a broad washacross the observer's eye 11, as depicted by arrows 20. The radiationreflected by the eye 11 is then focussed by the dynamic lens 12 onto thedetectors 18, as depicted by arrows 21. Thus, the dynamic lens 12 notonly functions to transmit to the observer's eye the image as displayedon the screen 10, but also forms an important part of the eye-tracker.The spatial frequencies of the emitters 17 and detectors 18 do not haveto be very high, but are sufficient to resolve the eye of the pupil orsome other ocular parameter.

FIG. 9 shows an alternative embodiment in which the dynamic opticalelement takes the form of a mirror 22 rather than a lens. In thisarrangement, the display screen 10 is interposed between the dynamicmirror 22 and the observer's eye, and is formed by a generallylight-transmitting screen 23 on which are provided a series of visiblelight emitters 24 (such as LEDs, lasers or phosphors) in red-green-bluetriads. The triads are spaced apart from one another, to permit the eye11 to view the displayed image after reflection by the dynamic mirror 22and subsequent passage through the screen 23. Each triad is fronted by amicro-lens array 25 which performs initial beam shaping.

The dynamic mirror 22 is based on the same diffractive opticalprinciples as the dynamic lens. The use of reflection techniques canoffer some advantages over a transmissive mode of operation because thedrive circuitry for the spatial light modulator can be implemented in amore efficient way, for example on a silicon backplane. As in the caseof the dynamic lens, the limited resolution of currently availablespatial light modulators will dictate that the mirror 22 is made up ofan array of miniature dynamic mirrors, each comprising a separatediffracting array. By arranging for the display screen 10 to have asuitably high pixel resolution, the displayed area of interest image canbe built up by generating a different field of view element for eachpixel, in a similar way to a dynamic lens. Alternatively, the image canbe generated by modulating the emitters 24 and synchronously modifyingthe diffracting patterns contained in the mirror 22 in such a way thatthe required image is produced by switching the direction of the emittedlight in the field of view. This has the advantage of requiring fewerelements in the partially transmitting panel 23 and hence allowing ahigher transmission. An equivalent approach can also be used in the casewhere the dynamic optical element is a lens.

FIG. 10 illustrates the application of the eye tracker to apparatus ofthe type shown in FIG. 9. More particularly, emitters 26 of radiation(such as infra-red light) are provided on the light transmitting screen23 and emit radiation towards the dynamic mirror 22. The mirror 22 thenreflects that radiation as a broad wash through the screen 23 and ontothe observer's eye 11, as depicted by arrows 27. Radiation reflected bythe eye 11 passes back through the screen 23 and onto detectors 28provided on the mirror 22. Other configurations are, however, possible.For example, both the emitters 26 and detectors 28 could be mounted onthe panel 23, with the dynamic mirror performing the functions ofreceiver and transmitter optics.

In the above-described embodiments, reference has been made to thespatial light modulator comprising a liquid crystal device. However,other types of spatial light modulator can also be used, such as surfaceacoustic wave devices and micro-mirror arrays.

In a further embodiment (shown in FIG. 11), the dynamic optical device12 takes yet another form, namely that of an electrically switchableholographic composite (ESHC). Such a composite (generally referenced200) comprises a number of layers 201, each of which contains aplurality of pre-recorded holographic elements 202 which function asdiffraction gratings (or as any other chosen type of optical element).The elements 202 can be selectively switched into and out of operationby means of respective electrodes (not shown), and sequences of theseelements 202 can be used to create multiple diffraction effects. ESHCshave the advantages of high resolution, high diffraction efficiency,fast switching time and the capability of implementation in non-planargeometries.

If a liquid crystal display, surface acoustic element or micromirrordevice is used, the dynamic optical device will operate on the basis ofdiscrete switchable elements or pixels. Although such a device can beprogrammed at pixel level, this is achieved at the expense of limitedresolution. As a result, it is difficult to achieve very highdiffraction efficiencies. In contrast, ESHCs have sub-micron resolution,which represents a substantially higher pixel density than that of theabove-described types of spatial light modulators. Typically, theresolution of conventional spatial light modulators are of the order of512², representing about one million bits of encoded data: thediffraction efficiencies tend to be well below 50%. In contrast, ESHCsoffer a resolution equivalent to 10¹³ bits, and diffraction efficienciesclose to 100% are therefore a practical proposition.

An ESHC may be defined as a holographic or diffractive photo polymericfilm that has been combined with a liquid crystal. The liquid crystal ispreferably suffused into the pores of the film, but can alternatively bedeposited as a layer on the film. The hologram may be recorded in theliquid crystal either prior to or after the combination with the photopolymeric film. Recordal of the hologram can be performed by opticalmeans, or by the use of highly accurate laser writing devices or opticalreplication techniques. The resultant composite typically comprises anarray of separate holograms that are addressed by means of an array oftransparent electrodes manufactured for example from indium tin oxide,which usually have a transmission of greater than 80%.

The thickness of the composite is typically 10 microns or less.Application of electric fields normal to the plane of the compositecauses the optical characteristics of the liquid crystals to be changedsuch that the diffraction efficiency is modulated. For example, in oneimplementation the liquid crystal is initially aligned perpendicularlyto the fringe pattern and, as the electric field is increased, thealignment swings into the direction with the effective refractive indexchanging accordingly. The diffraction efficiency can be either switchedor tuned continuously. Typically, the range of diffraction efficienciescovers the approximate range of 100% to 0.1%. There is therefore a verylarge range of diffraction efficiency between the “fully on” and “fullyoff” states of the ESHC, which makes the ESHC a very efficient switchingdevice.

The speed of response is high due to the encapsulation of the liquidcrystals in the micropore structure of the polymeric film. In fact, itis possible to achieve hologram switching times in the region of 1 to 10microseconds using nematic liquid crystals. Ultimately, very highresolutions can be achieved, with equivalent array dimensions of up to10⁵ and sub-micron spot sizes. It is even possible to approach thetheoretical ideal of a continuous kinoform.

Although the holographic diffraction patterns must be pre-recorded andcannot be altered, a limited degree of programmability is possible. Forexample, it is possible to programme diffraction efficiency and relativephase in arrays of holographic elements arranged in stacks and/oradjacent to each other. A multi-layer ESHC of this type is essentially aprogrammable volume hologram. Taking multiple diffraction into account,a wavefront passing through the device could be switched into 2^(N)output wavefronts, where the integer N represents the product of thenumber of layers and the number of elements in each layer. As anillustration of the capability of such a device, in the case of athree-level system with each plane having a resolution of 8×8 elements,the number of possible output wavefronts is 2¹⁹⁷ (or 10⁵⁷). Hence, thenumber of diffractive functions that can be implemented is practicallyunlimited. In practice, some of the layers in a stack would be providedwith electrodes, whilst others would operate in a passive state.

Each wavefront can be made to correspond to a particular gaze direction.Manifestly, not all of the wavefronts would be generated at the sametime because of the need for certain rays to use the same hologramsalong portions of their paths. However, by making the hologram arraysizes suitably large and taking advantage of the characteristic shortswitching time, the requisite number of wavefronts can be generated attypical video rates of 50 Hz.

For example, to provide one minute of arc display resolution over aninstantaneous eye track area of interest of size 10°×10°, a total of600×600 separate wavefronts would need to be generated in {fraction(1/50+L )} second, which is equivalent to 18×10⁶ separate wavefronts in20 milliseconds. Assuming that the input resolution of the portion ofthe hologram array stack that corresponds to the field of view is 30×30,and the entire holographic array can be switched in 1 microsecond, thenthe time required to generate the full set of wavefronts is equal to:

1×(18×10⁶)/(30×30)=20 milliseconds.

To provide the same resolution and switching time over the maximum humanmonocular field of view of 150°×135°, a holographic array would berequired with size equivalent to:

[(150/10)×30]×[(135/10)×30]=450×390.

By using a construction of the above-described type, it is also possibleto arrange for all of the holographic elements in a layer to be switchedsimultaneously, with the selection of specific holograms in the layersbeing performed by appropriate switching of the individuallight-emitting elements. Such “optical addressing” eliminates the wiringproblems posed by having several high resolution hologram matrices.Furthermore, by recording multiple Bragg patterns in a given hologram,the number of possible deviation patterns for a light beam passingthrough that hologram can be increased, thereby enabling the number oflayers in the ESHC to be reduced. The number of Bragg patterns that canbe multiplexed depends on the refractive index modulation that isavailable, typically up to around 20 multiplexed patterns are possible.This reduces the effects of scatter and stray light, whilst stray lightcan be further minimised by the use of anti-reflection coatings appliedto selected layers.

Because holograms are highly dispersive, the effects of chromaticaberration can be minimised by arranging for separate “channels” in theESHC for the primary wavelengths, so that each channel can be optimisedfor the particular wavelength concerned. The term “channel” is intendedto indicate a sequence of holographic elements through which the beampropagates. Also, chromatic aberration caused by the finite bandwidth ofthe light emitted by LEDs, can be reduced by employing suitable bandpass filters

An ESHC is typically a thick or volume hologram which is based on Braggdiffraction, giving a theoretical diffraction efficiency of 100%. Inprinciple, it is also possible to configure the ESHC as thin holograms(Raman-Nath regime), which can also give 100% efficiency in certaincircumstances.

FIG. 11A depicts an ESHC in which the holographic elements 202 insuccessive layers 201 become progressively more staggered towards theperiphery. This enables light rays (such as indicated at L) to bedeviated at the periphery of the ESHC through larger angles than wouldotherwise be possible.

FIG. 11B is a schematic illustration of the way in which a light beam L¹can be deflected through differing angles by reflection at the Braggsurfaces B of the holographic elements in successive layers 201 of theESHC. For example, L¹ denotes the path followed by a light beam which isdeflected by a Bragg surface in the first of the layers 201 only, whilstL¹ denotes the path followed by the same beam when the relevantholographic element in the next layer is activated so that the beam isdeflected by a Bragg surface in that element also.

In a further development, the dynamic optical device can operates amirror, for example by combining an ESHC device with conventionalsilicon backplane technology, such as is used in active matrix liquidcrystal displays.

As a further alternative, the dynamic optical device can take the formof a multi-layer liquid crystal divided into a number of individualcells, each of which is switchable between a limited number of states,which creates essentially the same effect as an ESHC.

In the above-described embodiments, the image for viewing by theobserver is generated by a display screen, in particular an LCD screen,although an electro luminescent screen or any other flat-panel screen(eg LED array) could be used instead. However, it is also possible touse other types of image generator. FIG. 12 shows one particularexample, in which the input image data is generated by modulating anarray of light emitting elements 250 (such as lasers or LEDs) at highfrequency and using an ESHC 251 as described above to “switch” the laserbeams between different orientations, such as indicated for laser beam252. The lasers in the array can be configured as triads of red, blueand green. A micro-optic beam-forming system such as micro lenses 253can be associated with the lasers.

FIG. 13 shows another example of the viewing apparatus, in which theimage generator takes the form of a light guide panel 260 having aseries of lasers 261 disposed around its periphery. Fabricated withinthe panel 260 are a series of prisms 262 each of which has an inclinedsemi-reflecting surface 263 confronting one of the lasers 261. Thesesurfaces 263 receive light from the lasers 261 and partially reflectthis in a direction normal to the panel 260. Microlenses 264 areprovided on a surface of the panel 260 which confronts the user, tofocus and/or shape the respective laser beams.

As an alternative to lasers, LEDs of suitably narrow wavelength bandscould be used. The lasers and/or LEDs can be fabricated from wide-bandsemiconductors such as GaN.

The image information is encoded by temporal modulation of the laserbeams, and therefore the resolution of the laser array does not need tobe large. This means that, by providing the laser array on a generallytransparent panel, the observer can have the facility of viewing thesurroundings. Furthermore, as shown in FIG. 12, it is possible toprovide an external shutter 270 (such as by means of an additional layerof liquid crystal) whereby the observer can switch the surroundings intoand out of view. In this manner, the observer can use the shutter toshut out external light whilst using the ESHC in diffractive mode toview a virtual display, or alternatively the shutter can be used totransmit light from the surroundings whilst switching the ESHC tonon-diffractive mode. As a further alternative, the virtual imagery andambient view can be superimposed in the manner of a head-up display.Under these circumstances, in order to avoid conflict with using thesame processing elements in the ESHC for both virtual and ambient imagescanning, the shutter liquid crystal can be provided as an array suchthat it is possible to switch off those pixels corresponding to field ofview directions at which virtual imagery is to be displayed.Alternatively, other techniques can be employed, such as those based onpolarisation, wavelength division, etc.

There are other ways in which a provision for viewing the surroundingscan be included in the apparatus. For example, in the case where theimage generator comprises an LCD or electro luminescent panel, gaps canbe left in the display layer. Also, in the case where an LCD is used, atransparent back-lighting arrangement can be used. A further alternativeis depicted in FIG. 14, wherein the display panel (referenced 280) ispivotally mounted on a headset 281 of which the apparatus forms part.The panel 280 can be pivoted between a first position (shown in brokenlines) in which it confronts the dynamic lens (referenced 282), and asecond position (shown in solid lines) in which it is disposed away fromthe lens 282 to allow ambient light to pass therethrough.

Another arrangement is shown in FIG. 15, wherein the display panel(referenced 290) does not allow ambient light to pass therethrough, andin which a detector array 291 is disposed on the external side of thepanel 290 so that the detectors therein face the surroundings through apanel 292 of lenses. The lenses in the panel 292 form images of thesurroundings on the detectors in the array 291, and signals receivedfrom the detectors are processed by a processor 293 for display on thedisplay panel 290. In this way, the user can switch the display on thepanel 292 between internal imagery and the surroundings, and view eitherof these by way of the dynamic lens (referenced 293).

In the above-described embodiments, the sensing means comprises emittersand detectors. The emitters emit radiation (such as infra-red radiation)which is projected as a broad wash onto the observer's eye, and theradiation scattered back from the eye is projected onto the detectors.On the one hand, the dynamic optical device functions not only to focusimage light onto the observer's eye, but also to project the radiationfrom the emitters onto the eye and/or to project the radiation reflectedby the eye to the detectors. On the other hand, the emitters and/or thedetectors are provided at pixel level within the field of view of theobserved image.

These general arrangements can be applied to viewing apparatuses otherthan those incorporating dynamic optical devices.

One such system is illustrated in FIGS. 16 and 16A, in which one or moreinfra-red emitters (referenced 300) are provided on a light-transmittingscreen 301 positioned forwardly of the display screen 10. Image light302 from the display screen 10 is directed to the observer's eye 11 bymeans of a lens system 303 (depicted schematically) which collimates theimage light over a field of view of typically 40°. Infra-red radiation304 from the emitter(s) 300 is projected as a broad wash onto thesurface of the eye 11 by the lens system 303 and is scattered thereby.The returned infra-red radiation 304 ¹ is propagated back through thelens system 303, and is projected onto an element 305 positionedimmediately in front of the display screen 10 which acts as a reflectorto infra-red wavelengths but not to visible light. The element 305 canfor example be a holographic or diffractive mirror, or a conventionaldichroic mirror. After reflection by the element 305, the infra-redradiation is projected onto the screen 301 as a focussed image of thepupil of the eye 11, and is incident upon one or more detectors 306provided at pixel level in or on the screen 301. The arrangement of theemitters 300 and detectors 306 is such as to cause minimal obstructionto the passage of the image light through the screen 301.

FIG. 16A shows a cross-section of the screen 301, on which the focussedpupil image is indicated by broken lines at 307. If (as shown) thedetectors 306 are arranged in an array in the shape of a cross, then thedimensions of the instantaneous image 307 can be measured in twoorthogonal directions, although other arrangements are also possible.

An alternative system is shown in FIG. 17, wherein a small number ofinfra-red emitters 400 (only one shown) are provided at pixel level inor on the display screen 10 itself. As in the embodiment of FIG. 16,image light 401 from the display screen 10 is directed to the observer'seye 11 by a lens system 402. In this embodiment, however, an inclinedbeamsplitter 403 is interposed between the display screen 10 and thelens system 402. Infra-red radiation 404 from the emitters 400 passesthrough the beamsplitter 403 and is projected by the lens system 402 asa broad wash onto the observer's eye 11 to be scattered thereby. Thereturned infra-red radiation 404 ¹ passes through the lens system 402and is then reflected by the beamsplitter 403 so that it is deflectedlaterally (either sideways or up or down) towards a relay lens system405, which projects the returned infra-red radiation onto an array ofdetectors 406 to form a focussed infra-red image of the pupil on thedetector array. Both the relay lens system 405 and the detector array406 are thus displaced laterally from the main optical path through theviewing apparatus. In the illustrated embodiment, the beamsplitter 403takes the form of a coated light-transmitting plate, but a prism can beused instead.

A further alternative arrangement is shown in FIG. 18, wherein one ormore infra-red emitters 500 are again incorporated at pixel level in oron the display screen 10. As before, image light 501 from the displayscreen 10 is focussed by a lens system 502 onto the observer's eye 11,with the lens system 502 collimating the visible light over a field ofview of typically 40°. However, in this embodiment there is positionedbetween the display screen 10 and the lens system 502 one or morediffractive or holographic elements 503 which are optimised forinfra-red wavelengths and which have minimal effect on the visible lightfrom the display screen 10. Thus, the focal length of the combinedoptical system comprising the element(s) 503 and the lens system 502 forvisible light is different from that for infra-red radiation. Thecombined effect of the element(s) 503 and the lens system 502 is toproduce a broad wash of infra-red radiation across the surface of theobserver's eye 11. Infra-red light scattered off the surface of the eyeis then projected by the combined effect of the lens system 502 and theelement(s) 503 onto the surface of the display screen 10 to form afocussed infra-red image of the pupil, which is detected by detectors505 (only one shown) also provided at pixel level in or on the displayscreen 10.

In the embodiments of FIGS. 16 to 18, the lens systems 303, 402 and 502are based on conventional refractive optical elements. However, theprinciples described can be applied to arrangements wherein a dynamicoptical device is used instead.

Also in the embodiments of FIGS. 16 to 18, the lens systems 303, 402 and502 perform the dual function of focussing the image light onto theobserver's eye and of focussing the returned infrared radiation onto thedetectors. The lens system must therefore cope with a wide variation ofdifferent wavelengths, and a lens system which has optimised performancewith respect to visible light may not perform exactly the desiredfunction with respect to infra-red radiation. In practice, the disparityis sufficiently small that it does not create a problem, particularly ifnear infra-red radiation is used. However, it is nevertheless sometimesdesirable to incorporate some form of compensation for the infra-redradiation, such as the incorporation of the element(s) 503 in theembodiment of FIG. 18.

In an alternative arrangement, instead of employing infra-red radiationfor eye tracking, it is possible to use light in the visible spectrum.This visible light could be rendered undetectable to the observer byusing the light in very short bursts, or by allocating specific elementsin the array for tracking (which could be colour-adjusted to match thesurrounding image elements), or by using specific narrow bands ofwavelengths.

The efficiency of the eye tracker will be limited by the latency of theprocessing system used to detect the variation in the ocular feature(such as the pupil edge, the dark pupil, etc) that is being used. Inorder to increase this efficiency, it is possible to use parallelprocessing techniques which can be implemented using hybridelectronic-optical technology, or even entirely optical processingmethods. By harnessing the full speed advantage of optical computing, itis possible to perform eye tracking such that the image generator onlyneeds to compute the data contained within the central 1° to 2° of theeye's field of view.

An optical computer for use with the present apparatus comprisescomponents such as switches, data stores and communication links. Theprocessing involves the interaction of the dynamic lens with theemitters and detectors. Many different optical processing architecturesare possible, the most appropriate types being those based on adaptivenetworks in which the processing functions are replicated at each node.It is even possible to combine the image generator, optical computingstructure and the dynamic lens into a single monolithic structure.

As explained above, a dynamic lens is a device based on diffractionprinciples whose optical form can be changed electronically. Forexample, this can take the form of a lens based on a binary profile, ora close approximation to the ideal kinoform, written onto a spatiallight modulator or similar device. Although the primary use of thedynamic lens is to vary the focal length, it can also serve otherfunctions such as to correct geometric distortions and aberrations. Forexample, chromatic aberrations can be reduced by re-calculating thediffraction pattern profiles (and hence the focal length) of the lensfor each primary wavelength in sequence. Alternatively, three associateddynamic lenses could be used, each optimised for a different primarywavelength. These lenses can be augmented by bandpass filters operatingat the primary wavelengths. In addition, the dynamic lens (inassociation with an input image array) can be used to vary the position,size and/or shape of the exit pupil in real time.

As a result of this, it is possible to achieve several advantageouseffects. Firstly, a wide field of view (FOV) can be created, which helpsrealism. This stems primarily from the ability to move the exit pupil.The ability to implement imaging functions within a relatively thinarchitecture also helps to eliminate many of the geometrical opticalobstacles to achieving high FOV displays. In contrast, in conventionaloptics a large exit pupil is achieved either by using mechanical meansto move a small exit pupil (which is generally not practical given theproblems of inertia, etc), or by using large numbers of optical elementsto correct aberrations, etc, with consequent complexity and expense.

Secondly, the apparatus can be made light in weight so that it iscomfortable and safe for a user to wear. This also means that theapparatus has low inertia, so the user has minimal difficulty in movinghis or her head while wearing the apparatus. The reduction in weightresults in part from the intrinsic lightness of the materials used tofabricate the spatial light modulator, as compared with those employedfor conventional optics.

Thirdly, the functions of image transmission and eye tracking arecombined into a single integral unit. This also assists in making theapparatus relatively low in weight. Furthermore, it also provides foreasy area of interest detection and detail enrichment, which enables aneffective high resolution to be achieved.

Fourthly, by suitably designing the software for driving operation ofthe dynamic lens, it is possible to prevent disassociation betweenaccommodation and convergence, so that the apparatus does not place avisual strain on the user and provides a more realistic display. This isto be contrasted with conventional optics which, even if the relevantrange information is available, are not capable of displaying objects atthe correct depth without incorporating moving parts in the opticalsystem or using other methods of changing the focal characteristics ofthe lenses.

A further advantageous property of the dynamic lens is its ability toreconfigure itself to allow different wavelength bands (e.g. visible andinfra-red) to propagate through it. Multiple wavelengths can betransmitted simultaneously, either by allocating different portions ofthe dynamic lens to different wavelengths, or by reconfiguring the lenssequentially for those wavelengths. Moreover, the direction ofpropagation of those different wavelengths does not have to be the same.This makes the dynamic lens particularly useful in on the one handtransmitting image light for viewing by the observer, and on the otherhand transmitting the infrared light used in the eye tracker system.

Although the above description makes particular reference to dynamiclenses, it will be appreciated that the principles expounded are equallyapplicable to dynamic mirrors.

FIG. 19 illustrates the basic concept of a dynamic lens operating ondiffraction principles. The display screen 10 embodies a number ofinfra-red emitters 600 at pixel level, and a series of diffractionpatterns 601 are generated in a spatial light modulator 602 which servethe function of lenses, to focus image light 603 from the display screen10 onto the observer's eye and to project the infra-red light 604 fromthe emitters 600 as a broad wash onto the surface of the eye 11.

In order to reduce the burden on the dynamic lens and facilitate thediffraction calculations that are required in order to re-configure thespatial light modulator each time the display is updated, it is possibleto transform or distort the image as actually displayed on the displayscreen 10. Under these circumstances, the distinction between the inputimage display and the dynamic optical device becomes less well defined.

FIG. 20 illustrates a further development of the invention, in which thefunctions of image generation and dynamic imaging are combined within adynamic holographic element 700. The required output image is thenproduced by reconstruction using only a series of reference beamsproduced by an array of discrete light sources 701. In the illustratedarrangement, the light sources 701 are mounted on a screen 702 disposedbehind the dynamic holographic element 700, on which are also providedinfra-red emitters 703 and detectors 704 for the eye tracking function.

The screen 702 thus performs no imaging function, i.e. it has nopictorial content, its purpose being merely to provide a set ofreference beams. The resolution of the array of reference beam sources701 can in fact be quite low, although the economy of design thatresults is achieved at the expense of the additional computational powerrequired to re-calculate the hologram for each image update, since boththe lens function and the image need to be recomputed.

The dynamic holographic element 700 can be implemented using a highresolution spatial light modulator such as that based on liquidcrystals, micro-mechanical mirror arrays or opto-acoustic devices. It ispossible for the dynamic hologram to operate either in transmission orin reflection. As is the case where a separate dynamic optical deviceand image generator are used, the use of reflective techniques can offercertain advantages, such as in allowing circuitry to be implemented in amore efficient way, and in enhancing the brightness of the display.

It is also possible to incorporate into the dynamic hologram lenseswhich project infra-red light from the emitters 703 onto the observer'seye, these lenses being encoded within portions of the hologram.

In a further modification (not shown), a texturised screen is providedaround the periphery of the image displayed on the display screen. Forreasons that are not yet fully understood, it has been found that theuse of such a texturised screen can induce an illusion of depth in thedisplayed image, and this effect can be used to enhance the reality ofthe image as perceived by the user. The screen can be provided as aseparate component which surrounds or partially overlies the peripheryof the display screen. Alternatively, a peripheral region of the displayscreen itself can be reserved to display an image replicating thetexturised effect. Moreover, under these circumstances it is possible toalter the display in that peripheral region to vary the texturisedeffect in real time, to allow for changes in the image proper asdisplayed on the screen and adjust the “pseudo-depth” effect inaccordance with those changes.

In the above embodiments, the display screen and dynamic lens aredescribed as being curved. However, as depicted in FIGS. 21 and 21A, itis possible to construct the display screen 10 from a series of planarpanels 900, and similarly to construct the dynamic lens 12 from a seriesof panels 901, each panel 900 and 901 being angled relative to itsneighbour(s) so that the display screen and dynamic lens eachapproximate to a curve. FIG. 21A shows the configuration of the screen10 and lens 12 in three dimensions.

Referring now to FIGS. 22 and 23, there is shown apparatus for viewingan image which is generally similar to that depicted in FIG. 12. Theapparatus comprises an image generator 1010 in the form of an array ofLED triads 0101 provided on a generally light-transmitting screen 1012.The LED triads 1011 form a low resolution matrix of, say, 100×100 or200×200 elements. Light from the LED triads 1011 is subjected to beamshaping by a microlens array 1013, and then passes through a liquidcrystal shutter 1014 towards an ESHC 1015. The microlens array 1013 hasas its main effect the collimation of the light emitted by the LEDtriads 1011, and can be of holographic design.

The LEDs in the triads 1011 are driven by signals defining an image tobe viewed by an observer. On the one hand, these signals are such thatthe array of LEDs produces a relatively coarse version of the finalimage. On the other hand, the signals supplied to each LED triad aretime-modulated with information referring to image detail, and the ESHC1015 functions to scan the light from that triad in a manner whichcauses the image detail to be perceived by the observer.

The apparatus also comprises an eye tracker device which senses thedirection of gaze of the observer's eye. Suitable forms of eye trackerare described above and are not shown in any detail herein. Suffice itto say that radiation from a plurality of emitters is projected onto theobserver's eye in a broad wash, and radiation reflected back from theeye is projected onto detectors, such as detector elements 16 mounted inor on the screen 1012. The same optics as employed for imagetransmission are also used for the purpose of projecting the radiationonto the eye and/or projecting the reflected radiation onto the detectorelements 1016.

As indicated above, the eye tracker senses the direction of gaze of theobserver's eye. The operation of the ESHC 1015 is then controlled inaccordance therewith, so that the ESHC functions to “expand” theresolution of the initially coarse image only in the direction in whichthe eye is looking. In all other areas of the image, the resolution ismaintained at the initial coarse level. As the direction of gaze alters,the operation of the ESHC is changed as appropriate to “expand” theresolution in the new direction of gaze instead.

The liquid crystal shutter 1014 is switchable between two states, in thefirst of which the shutter is generally light-obstructing but containswindows 1017 for transmission of the light from the respective LEDtriads 1011. Within these windows, the liquid crystal material cancontrol the phase of the light beams, for example to create fine-tuningof the collimation of those beams. In its second state, the shutter 1014is generally light-transmitting and allows viewing of the ambientsurroundings through the screen 1012, either separately from or inconjunction with viewing of the image from the LEDs.

The ESHC 1015 can include passive holograms (i.e. not electricallyswitched) that are written onto the substrates, to allow for greaterflexibility in optimising the optical performance of the apparatus.

Instead of LEDs, the image generator 1010 can employ lasers.

As can be seen to advantage in FIG. 23, this form of constructionenables a very compact monolithic arrangement to be achieved, comprisinga succession of layers as follows:

the screen 1012 containing the LED/laser array

the microlens array 1013 embodied within a spacer

the liquid crystal shutter 1014

the ESHC 1015 comprising successive layers of holographic material 1018plus electrodes, and spacers 1019 between these layers.

The first spacer 1019 in the ESHC (i.e. that directly adjacent to theliquid crystal shutter 1014) allows for development of the light beamsfrom the LED triads after passing through the microlens array 1013 andbefore passing through the ESHC proper.

It is anticipated that the overall thickness of the apparatus can bemade no greater than about 7.5 mm, enabling the apparatus to beincorporated into something akin to a pair of spectacles.

FIG. 24 shows a modified arrangement wherein the apparatus is ofgenerally curved configuration, the curve being centred generally on anominal eye point 1020. Typically, the radius curvature of the apparatusis about 25 mm.

FIG. 25 shows an alternative arrangement, which operates on reflectiveprinciples. In this embodiment, the image generator 1040 comprises alight guide 1041 disposed on a side of the apparatus adjacent to theobserver's eye. The light guide 1041 is depicted in detail (in curvedconfiguration) in FIG. 26, and has a series of LEDs or lasers 1042disposed around its periphery. Lens elements 1043 (only one shown) areformed on the periphery of the light guide 1041, and each serves tocollimate the light from a respective one of the LEDs/lasers 1042 toform a beam which is projected along the guide 1041 through the bodythereof. Disposed at intervals within the guide 1041 are prismaticsurfaces 1044 (which can be coated with suitably reflective materials),which serve to deflect the light beams laterally out of the light guide1041.

Disposed behind the light guide 1041 (as viewed by the observer) are, inorder, a first ESHC 1045, a light-transmitting spacer 1046, a secondESHC 1047, a further light-transmitting spacer 1048, and a reflector1049 (which is preferably partially reflecting). Light emerging from thelight guide 1041 is acted on in succession by the ESHCs 1045 and 1047,is reflected by the reflector 1049, passes back through the ESHCs 1047and 1045 and finally through the light guide 1041 to the observer's eye1050. Because the light undertakes two passes through each of the ESHCs1045 and 1047, this gives more opportunity for control of the beampropagation.

In practice, the apparatus shown in FIG. 25 can also include a microlensarray and a liquid crystal shutter such as those described above withreference to FIGS. 22 and 23, but these have been omitted forconvenience of illustration.

FIGS. 27A to 27C show in schematic form alternative configurations forthe apparatus. In FIG. 27A, the image generator comprises an array ofLEDs or lasers 1050 provided in or on a light transmitting screen 1051.As with the arrangement depicted in FIG. 25, the screen 1051 is disposedon a side of the apparatus adjacent to the observer's eye 1052. Lightfrom the LEDs/lasers 1050 is initially projected away from the eye 1052through an ESHC 1053, and is then reflected by a reflector 1054 backthrough the ESHC 1053. The light then passes through the screen 1051 andpasses to the observer's eye. Again, this arrangement has the advantagethat the light passes through the ESHC 1053 twice, giving increasedopportunity for the control of the light beam shaping.

FIG. 27B shows in schematic terms an arrangement similar to that alreadydescribed with reference to FIGS. 22 and 23, but wherein the imagegenerator comprises a light guide 1055 of the general type shown in FIG.26. FIG. 27C shows a similar arrangement, but wherein the light guide isreplaced by a light-transmitting screen 1056 having an array of LEDs orlasers 1057 therein or thereon.

As with FIG. 25, the microlens array and the liquid crystal shutter havebeen omitted from the drawings for ease of illustration, but will inpractice be provided between the image generator and the ESHC in eachcase.

All of these arrangements are capable of being implemented as amonolithic, very thin panel (typically less than 10 mm in thickness). Inpractice, the overall thickness of the panel will be dictated by therequired thickness of the substrates and spacers.

The use of a light guide such as described with reference to FIGS. 25,26 and 27B can offer a greater degree of transparency to the imagegenerator for viewing of the ambient surroundings.

As depicted in FIG. 28, the apparatus can also be adapted for use bymultiple observers, by arranging for the dynamic optical device(referenced 1070) to create more than one exit pupil, one for each ofthe intended observers. Reference numeral 1071 denotes an imagegenerator comprising an array of LEDs/lasers 1072 on a screen 1073,which screen also incorporates emitters 1074 and detectors 1075 of theeye tracking system. Signals received from the detectors 1075 areprocessed by a processor 1076 and a multiple-target tracking system 1077which detects the positions of the heads of the various observers. Thecharacteristics of the dynamic optical device 1070 are then altered inaccordance with the detected head positions and directions of gaze, tocreate suitable exit pupils for viewing by the observers of the imagetransmitted by the image generator 1071.

The apparatus can also be adapted for the viewing of stereoscopicimages. For example, as shown in FIG. 29, a pair of apparatuses asdescribed can be mounted side by side in a headset 1100. Each apparatuscomprises generally an image generator 1101 (such as a display screen),a dynamic optical device 1102 and an eye tracker 1103. Stereoscopicallypaired images are produced by the image generators 1101, and are viewedby the observer's eyes 1104 respectively by means of the respectivedynamic optical devices 1102. Each eye tracker 1103 senses the directionof gaze of the respective eye 1104, and the respective dynamic opticaldevice 1102 maintains an area of high resolution in that direction ofgaze, and alters this as the direction of gaze changes.

In an alternative arrangement (shown in FIG. 30), a single dynamicoptical device 1102 ¹ is used in common to both apparatuses, and acts tocreate two areas of high resolution corresponding to the directions ofgaze of the observer's eyes 1104, respectively. Under thesecircumstances, it may be possible to employ a single eye tracker 1103which detects the direction of gaze of one eye 1104. One area of highresolution is created using signals obtained directly from the eyetracker, while the other area of high resolution is created inaccordance with signals received from the eye tracker 1103 andinformation in the image input signal.

FIG. 31 shows a further embodiment of the invention in which the displayscreen (referenced 1201) is of a different form. In, for example, theembodiment of FIG. 12 the display screen comprises a monolithic LEDarray on a substrate. The size of this array is equivalent to a 768×768matrix on a 60 mm substrate and, whilst this is not a particularly largematrix in purely numerical terms, the need to cluster the LEDs in asmall area can pose difficulties due to the high density of wiringrequired. Also, the presence of this wiring on the substrate will havethe effect of reducing the intensity of the light passing therethroughwhen the apparatus is used in a mode to view the surroundings.

The arrangement depicted in FIG. 31 is intended to solve this particulardifficulty by employing photon generation modules 1202 which aredisposed around the periphery of a transparent plate 1203. Each module1202 is built up from a number of separate, lower resolution arrays ofLEDs, as will be described later. The plate 1203 is moulded fromplastics material and includes light guides 1204 and miniature lenses(not shown in FIG. 31) which are used to relay demagnified images of theLED arrays to each of a number of nodes 1205 situated directly in frontof the microlens array (referenced 1206). Reference numeral 1207designates the ESHC, while reference numerals 1208 indicate typicaloutput light beams produced by the apparatus.

FIG. 32 shows a front view of the display screen 1201, wherein thepositioning of light guides 1204 and nodes 1205 (six in all) can be seento advantage. Reference numeral 1209 designates an opaque region inwhich the photon generation modules 1202 are located.

Mounting the photon generation modules 1202 around the periphery of theplate 1203 also solves the problem of decreasing geometric blur due tothe finite size of the LED elements, since the ratio of pixel size toLED/microlens array distance must be kept small. Furthermore, the plate1203 does not now have to be made of a suitable LED substrate material,and can simply be made of optical-grade plastics.

FIG. 33 shows the construction and operation of one LED array of aphoton generation module 1202 in detail. More particularly, the LEDarray is disposed parallel to the plate 1203, and light emittedtherefrom is subjected to initial beam shaping by an optical element1210 such as a holographic diffuser The light is then reflected through90° inwardly of the plate 1203 by a reflector element 1211, and passesin sequence through a relay lens 1213, a focussing element 1214 (forexample an LCD element) and a condenser lens 1215. The light then passesalong the respective light guide 1204 to the respective node 1205, whereit is deflected by a reflector element 1216 towards the microlens array1206. On leaving the plate 1203, the light is spread by a beam divergingelement 1217 provided on the surface of the plate 1203 confronting themicrolens array 1206.

As indicated above, each of the photon generation modules 1202 is formedof a cluster of LED arrays. A typical example is shown in FIG. 34,wherein the module comprises four arrays 1221 each containing a 50×50matrix of LEDs measuring 4 mm×4 mm. Because each of the arrays 1221subtends a slightly different angle to the associated optics, the beamsgenerated by the four arrays emerge at slightly different angles fromthe respective node 1205. This can be used to achieve a small amount ofvariation in the direction of the output beam for each channel of lightpassage through the assembly of the microlens array 1206 and the ESHC1207.

FIG. 35 is a schematic view of apparatus embodying the above-describeddesign of display panel, illustrating the typical passage therethroughof an output beam 1218. The display panel 1201 is mounted on one side ofa transparent light guide panel 1219, the panel 1219 having the array ofmicrolenses 1206 mounted on its other side. An LCD shutter 1220 isdisposed between the microlens array 1206 and the ESHC 1207. In thisembodiment, the microlens array 1206 comprises a 36×36 array ofindependently switchable holographic microlenses, and the ESHC 1207comprises a stack of substrates each containing a 36×36 array ofsimultaneously addressable holograms.

FIGS. 36 and 36A show an alternative arrangement wherein a single photongeneration module (referenced 1301) is employed in common betweendisplay screens 1302 for viewing by the observer's two eyes,respectively. The module 1301 operates on essentially the sameprinciples as that described in the embodiment of FIGS. 31 to 34, and isdisposed intermediate the two display screens 1302. Each display screen1302 includes light guides 1303 and nodes 1304 as before, the nodes 1304in this instance being formed by curved mirrors 1305.

FIG. 36B shows schematically a manner in which the photon generationmodule can be implemented in this arrangement. More particularly lightfrom an LED array 1401 contained in the module is subjected to beamshaping by a lens 1402 and then passes through a liquid crystal array1403. The beam then passes to a fixed grid 1404 which operates ondiffraction principles to produce a plurality of output beams 1405 atdefined angles, and the above-mentioned light guides are configured tomatch those angles.

Referring now to FIGS. 37 and 38 a viewing apparatus 1500 includes animage generator 1501 arranged to emit light into projection optics 1502.The projection optics 1502 are arranged to project light from the imagegenerator towards a dynamic optical element 1503, arranged at an acuteangle with a principal axis of the projection optics 1502. The dynamicoptical element 1503 is generally reflective, and is controlled by acontroller 1504.

The dynamic optical element 1503 causes an image to be formed such thatan observer 1505 viewing the image experiences a wide field of view. Forclarity, tracking apparatus is not shown on the embodiment soillustrated, but it will be appreciated that eye tracking apparatus canbe arranged therein.

The off axis orientation of the arrangement is best illustrated in FIG.38. As shown in that drawing, the dynamic optical element comprises Red,Green and Blue holographic layers 1503R, 1503G, 1503B. By enabling theselayers sequentially, the element 1503 can present a full colour image toa user.

When a layer is disabled, it is transparent. It will be understood fromthe above description that that arrangement is necessary because of themonochromatic nature of holographic elements. The high angle ofincidence of light on to the dynamic optical element 1503 from the imagegenerator 1501 and projection optics 1502 is clearly illustrated. Itwill be appreciated that the Red, Green and Blue channels of the elementcan be interspaced in one layer as an alternative.

Located behind the dynamic optical element 1503 is an ambient lightshutter 1509. The ambient light shutter 1509 is operative, on receivinga stimulus from the controller 1504 to permit or to obstruct the passageof ambient light through the dynamic optical element. The gives the userthe facility to mix the display from the image generator 1501 with thereal-life view beyond the viewing apparatus 1500.

FIG. 39 illustrates an alternative arrangement which utilises atransmissive dynamic optical element 1503′. All other components areassigned the same reference numbers as in FIGS. 37 and 38. Evidently,the observer 1505 now views the image from the opposite side of thedynamic optical element than the image generator 1501 and projectionoptics 1502.

FIG. 40 illustrates how the dynamic optical device 1503 can comprise aletterbox shutter layer. The letterbox shutter layer is omitted fromFIGS. 38 and 39 for clarity. The dynamic optical device 1503 defines anarray of microlenses 1506. The shutter layer is electronicallycontrolled, such that for a given electronic signal a rectangular areaor letterbox 1507 of the shutter layer becomes transparent, theremainder of the shutter layer remaining opaque. The letterbox 1507 isregistered with a row of microlenses 1506. It may be registered withpart of a row, or other combination of microlenses, if desired. In thatway, by sequentially rendering specific areas 1507 of the shutter layertransparent, specific rows of the microlenses 1506 are exposed to light1508 from the projection optics 1502. This reduces the possibility ofaccidental beam spillage over onto adjacent microlenses from those forwhich the beam is intended. In that way the quality of the viewed imageis improved.

By virtue of the inherent angular selectivity of Bragg (volume)holograms, stray light which is predominantly parallel to the generalplane of the shutter alignment, and which does not satisfy the Braggcondition will be undeflected. In this plane, the undeflected light willpass out of the field of view of the observer due to the off-axisarrangement, and thus the quality of the final viewed image can beimproved.

The viewing apparata described above have many and varied applications,although they are designed primarily for use as head-mounted pieces ofequipment. In a particular example, the equipment includes two suchapparata, one for each eye of the user. In the entertainment field, theequipment can be used for example to display video images derived fromcommercially-available television broadcasts or from video recordings.In this case, the equipment can also include means for projecting theassociated soundtrack (e.g. in stereo) into the user's ears.

Also, by displaying stereoscopically paired images on the twoapparatuses, the equipment can be used to view 3-D television. Inaddition, by arranging for the projected images substantially to fillthe whole of the field of view of each eye, there can be provided alow-cost system for viewing wide field films.

In the communications sector, the apparatus can be used as an autocuefor persons delivering speeches or reading scripts, and can be used todisplay simultaneous translations to listeners in other languages. Theapparatus can also be used as a wireless pager for communicating to theuser.

In another area, the apparatus can be used as a night-vision aid or asan interactive magnifying device such as binoculars. Also, the apparatuscan be employed in an interactive manner to display a map of the area inwhich the user is located to facilitate navigation and route-finding.

Further examples demonstrating the wide applicability of the apparatusinclude its use in computing, in training, and in providing informationto an engineer e.g. for interactive maintenance of machinery. In themedical sector, the apparatus can be used as electronic glasses and toprovide disability aids. The apparatus can further be utilised toprovide head-up displays, for example for use by aircraft pilots and byair traffic controllers.

What is claimed is:
 1. Apparatus for viewing an image, comprising: animage generator; a dynamic optical device, the dynamic optical beingoperative to create a modulation in respect of at least one of phase andamplitude in light of the image received thereby, said modulation beingvariable from one point or spatial region in the optical device toanother, and; a control circuit operative to apply a stimulus to thedynamic optical device, whereby the modulation at any point or spatialregion can be varied, the control circuit being operative to alterperiodically the characteristics of the dynamic optical device so thatthe device acts sequentially to direct received, modulated image lightof different colors to an observer's eye, wherein the image generator isconfigured off-axis from the general direction of view of the observer'seye in use; wherein the apparatus is embodied in a headset with a sideportion arranged to be placed in the temple region of an observer'shead, the image generation generator being housed within the sideportion.
 2. Apparatus for viewing an image, comprising: an imagegenerator; a dynamic optical device, the dynamic optical device beingoperative to create a modulation in respect to at least one of phase andamplitude in light of the image received thereby, said modulation beingvariable from one point or spatial region in the optical device toanother, and a control circuit operative to apply a stimulus to thedynamic optical device, whereby the modulation at any point or spatialregion can be varied, the control circuit being operative to alterperiodically the characteristics of the dynamic optical device so thatthe device acts sequentially to direct received, modulated image lightof different colors to an observer's eye; wherein the apparatus includesleft and right image generators, left and right dynamic optical devicesand left and right side portions within which said left and right imagegenerator are housed, said left and right image generator beingoperative to project image light towards said left and right dynamicoptical devices respectively, thereby displaying a binocular image. 3.Apparatus for viewing an image, comprising: an image generator; adynamic optical device, the dynamic optical device being operative tocreate a modulation in respect of at least one of phase and amplitude inlight of the image received thereby, said modulation being variable fromone point or spatial region in the optical device to another, and acontrol circuit operative to apply a stimulus to the dynamic opticaldevice, whereby the modulation at any point or spatial region can bevaried, the control circuit being operative to alter periodically thecharacteristics of the dynamic optical device so that the device actssequentially to direct received, modulated image light of differentcolors to an observer's eye; wherein the dynamic optical device actsupon image light received and transmitted there through, and the imagegenerator is located on a side of the dynamic optical device remote fromthe intended position of the observer's eye.
 4. Apparatus for viewing animage, comprising: an image generator; a dynamic optical device, thedynamic optical device being operative to create a modulation in respectof at least one of phase and amplitude in light of the image receivedthereby, said modulation being variable from one point or spatial regionin the optical device to another, and a control circuit operative toapply a stimulus to the dynamic optical device, whereby the modulationat any point or spatial region can be varied, the control circuit beingoperative to alter periodically the characteristics of the dynamicoptical device so that the device acts sequentially to direct received,modulated image light of different colors to an observer's eye; whereinthe dynamic optical device acts upon image light received and reflectedthereby, and the image generator is at least partiallylight-transmitting and is located between the dynamic optical device andthe intended position of the observer's eye.
 5. Apparatus for viewing animage, comprising: an image generator; a dynamic optical device, thedynamic optical device being operative to create a modulation in respectof at least one of phase and amplitude in light of the image receivedthereby, said modulation being variable from one point or spatial regionin the optical device to another, and a control circuit operative toapply a stimulus to the dynamic optical device, whereby the modulationat any point or spatial region can be varied, the control circuit beingoperative to alter periodically the characteristics of the dynamicoptical device so that the device acts sequentially to direct received,modulated image light of different colors to an observer's eye; whereinthe dynamic optical device functions to correct aberration and/ordistortions in the image light received from the image generator. 6.Apparatus for viewing an image, comprising: an image generator; adynamic optical device, the dynamic optical device being operative tocreate a modulation in respect to at least one of phase and amplitude inlight of the image received thereby, said modulation being variable fromone point or spatial region in the optical device to another; a controlcircuit operative to apply a stimulus to the dynamic optical device,whereby the modulation at any point or spatial region can be varied, thecontrol circuit being operative to alter periodically thecharacteristics of the dynamic optical device so that the device actssequentially to direct received, modulated image light of differentcolors to an observer's eye; a first sensor operative to sense thedirection of gaze of the observer's eye, the control circuit beingoperative on the dynamic optical device to create an area of relativelyhigh resolution in said direction of gaze, the dynamic optical deviceproviding a lesser degree of resolution of the image elsewhere, thecontrol circuit being responsive to the first sensor and being operativeto alter the characteristics of the dynamic optical device to repositionsaid area of relatively high resolution to include said direction ofgaze as the latter is altered; wherein the first sensor comprises aradiation emitter operative to emit radiation for projection onto theobserver's eye and a detector operative to detect radiation reflectedback from the eye; wherein the radiation emitter and/or the detector areprovided on a light-transmitting screen disposed between the imagegenerator and the dynamic optical device.
 7. Apparatus as claimed inclaim 6, wherein the image generator is in the form of a display screen,and the radiation emitter and/or the detector are provided in or on thedisplay screen.
 8. Apparatus as claimed in claim 7, wherein theradiation emitter are provided in or on the display screen, a beamsplitter device is disposed between the display screen and the dynamicoptical device and is operative to deflect radiation reflected by theobserver's eye laterally of a main optical path through the apparatus,and the detector are displaced laterally from the main optical path. 9.Apparatus for viewing an image comprising: an image generator; a dynamicoptical device, the dynamic optical device being operative to create amodulation in respect of at least one of phase and amplitude in light ofthe image received thereby, said modulation being variable from onepoint or spatial region in the optical device to another; a controlcircuit operative to apply a stimulus to the dynamic optical device,whereby the modulation at any point or spatial region can be varied, thecontrol circuit being operative to alter periodically thecharacteristics of the dynamic optical device so that the device actssequentially to direct received, modulated image light of differentcolors to an observer's eye; a first sensor operative to sense thedirection of gas of the observer's eye, the control circuit beingoperative on the dynamic optical device to create an area of relativelyhigh resolution in said direction of gaze, the dynamic optical deviceproviding a lesser degree of resolution of the image elsewhere, thecontrol circuit being responsive to the first sensor and being operativeto alter the characteristics of the dynamic optical device to repositionsaid area of relatively high resolution to include said direction ofgaze as the latter is altered; wherein the first sensor comprises aradiation emitter operative to emit radiation for projection onto theobserver's eye and a detector operative to detect radiation reflectedback from the eye wherein the image generator produces a pixilatedimage, and the radiation emitter and/or detector are provided at pixellevel within the field of view.
 10. Apparatus for viewing an image,comprising: an image generator; a dynamic optical device, the dynamicoptical device being operative to create a modulation in respect of atleast one of phase and amplitude in light of the image received thereby,said modulation being variable from one point or spatial region in theoptical device to another; a control circuitry operative to apply astimulus to the dynamic optical device, whereby the modulation at anypoint or spatial region can be varied, the control circuit beingoperative to alter periodically the characteristics of the dynamicoptical device so that the device acts sequentially to direct received,modulated image light of different colors to an observer's eye; a firstsensor operative to sense the direction of gaze of the observer's eye,the control circuit being operative on the dynamic optical device tocreate an area of relatively high resolution in said direction of gaze,the dynamic optical device providing a lesser degree of resolution ofthe image elsewhere, the control circuitry being responsive to the firstsensor and being operative to the alter the characteristics of thedynamic optical device to reposition said area of relatively highresolution to include said direction of gaze as the latter is altered;wherein the first sensor utilizes infra-red radiation; at least oneoptical element provided in tandem with the dynamic optical device,which acts upon infra-red light but not upon visible light. 11.Apparatus for viewing an image, comprising: an image generator; adynamic optical device, the dynamic optical device being operative tocreate a modulation in respect of at least one of phase and amplitude inlight of the image received thereby, said modulation being variable fromone point or spatial region in the optical device to another; a controlcircuit operative to apply a stimulus to the dynamic optical device,whereby the modulation at any point or spatial region can be varied, thecontrol circuitry being operative to alter periodically thecharacteristics of the dynamic optical device so that the device actssequentially to direct received, modulated image light of differentcolors to an observer's eye; a first sensor operative to sense thedirection of gaze of the observer's eye, the control circuitry beingoperative on the dynamic optical device to create an area of relativelyhigh resolution in said direction of gaze, the dynamic optical deviceproviding at lesser degree of resolution of the image elsewhere, thecontrol circuit being responsive to the first sensor and being operativeto alter the characteristics of the dynamic optical device to repositionsaid area of relatively high resolution to include said direction ofgaze as the latter is altered; wherein the first sensor utilizesinfra-red radiation wherein the detector is provided on a lighttransmitting screen disposed between the image generator and the dynamicoptical device.
 12. Apparatus as claimed in claim 11, wherein areflector is disposed between the image generator and thelight-transmitting screen, and is operative to reflect the infra-redradiation whilst allowing transmission of visible light, such that theinfra-red radiation after reflection by the observer's eye passesthrough the dynamic optical device and the light-transmitting screen,and is reflected by said reflector back towards the screen. 13.Apparatus for viewing an image, comprising: an image generator; adynamic optical device, the dynamic optical device being operative tocreate a modulation in respect of at least one of phase and amplitude inlight of the image received thereby, said modulation being variable fromone point or spatial region in the optical device to another; a controlcircuit operative to apply a stimulus to the dynamic optical device,whereby the modulation at any point or spatial region can be varied, thecontrol circuit being operative to alter periodically thecharacteristics of the dynamic optical device so that the device actssequentially to direct received, modulated image light of differentcolors to an observer's eye; a first sensor operative to sense thedirection of gaze of the observer's eye, the control circuit beingoperative on the dynamic optical device to create an area of relativelyhigh resolution in said direction of gaze, the dynamic optical deviceproviding a lesser degree of resolution of the image elsewhere, thecontrol circuitry being responsive to the first sensor and beingoperative to alter the characteristics of the dynamic optical device toreposition said area of relatively high resolution to include saiddirection of gaze as the latter is altered wherein the first sensorutilizes visible light; wherein the visible light is utilized in shortbursts.
 14. Apparatus as claimed in claim 13, wherein the monolithicstructure also includes a micro-optical device operative to performinitial beam shaping.
 15. Apparatus for viewing an image, comprising: animage generator; a dynamic optical device, the dynamic optical devicebeing operative to create a modulation in respect of at least one ofphase and amplitude in light of the image received thereby, saidmodulation being variable from one point or spatial region in theoptical device to another; a control circuit operative to apply astimulus to the dynamic optical device, whereby the modulation at anypoint or spatial region can be varied, the control circuit beingoperative to alter periodically the characteristics of the dynamicoptical device so that the device acts sequentially to direct received,modulated image light of different colors to an observer's eye; a firstsensor operative to sense the direction of gaze of the observer's eye,the control circuit being operative on the dynamic optical device tocreate an area of relatively high resolution in said direction of gaze,the dynamic optical device providing a lesser degree of resolution ofthe image elsewhere, the control circuit being responsive to the firstsensor and being operative to alter the characteristics of the dynamicoptical device to reposition said area of relatively high resolution toinclude said direction of gaze as the latter is altered wherein thefirst sensor utilises visible light; wherein the first sensor includes alight emitter means operative to emit light for projection onto theobserver's eye, the image generator produces a pixilated image, theemitter is provided at a pixel level within the field of view, and thewavelength of light emitted by the light emitter is matched to that ofthe surrounding pixels in the generated image.
 16. Apparatus for viewingan image, comprising: an image generator; a dynamic optical device, thedynamic optical device being operative to create a modulation in respectof at least one of phase and amplitude in light of the image receivedthereby, said modulation being variable from one point or spatial regionin the optical device to another; a control circuitry operative to applya stimulus to the dynamic optical device, whereby the modulation at anypoint or spatial region can be varied, the control circuitry beingoperative to alter periodically the characteristics of the dynamicoptical device so that the device acts sequentially to direct received,modulated image light of different colors to an observer's eye; a firstsensor operative to sense the direction of gaze of the observer's eye,the control circuitry being operative on the dynamic optical device tocreate an area of relatively high resolution in said direction of gaze,the dynamic optical device providing a lesser degree of resolution ofthe image elsewhere, the control circuit being responsive to the firstsensor and being operative to alter the characteristics of the dynamicoptical device to reposition said area of relatively high resolution toinclude said direction of gaze as the latter is altered wherein thefirst sensor utilizes visible light; wherein the visible light isutilized in specific narrow band of wavelengths.